The capability of an aircraft to fly at hypersonic speeds places significant demands on the aircraft's propulsion system, since the aircraft must also fly slow enough to land and produce thrust for take off when the aircraft has zero velocity. One propulsion system that has been proposed for such applications is a combined-cycle engine.
One known combined-cycle engine, the Pratt & Whitney J58, utilizes a turbojet engine and is used to power the Lockheed SR71 Blackbird. The J58 turbojet operates as a conventional afterburning turbojet engine until it reaches a predetermined speed. Thereafter, bypass tubes are opened to bypass the air flowing into the engine around the compressor, burner and turbine. In this mode, the afterburner is activated so that the engine functions as a ramjet.
Other configurations for combined-cycle engines have been suggested wherein a turbojet or rocket engine is initially employed to provide thrust to permit the vehicle to take-off and attain a predetermined transition velocity and thereafter a dedicated ramjet engine is activated and the turbojet or rocket engine is deactivated so that only the ramjet engine produces propulsive thrust.
One drawback associated with the known combined cycle engines concerns the construction of the combustor that is used by the ramjet engine. More specifically, the combustors that are employed by the known combined cycle engines are relatively inefficient, heavy and large, usually having a length-to-diameter (L/D) ratio of about 5.0 to about 3.0.
As those skilled in the art will appreciate, improvements in the efficiency of the combustor and/or reductions in the weight and/or size of the combustor would permit a corresponding improvement in the range and/or payload capacity of an aircraft utilizing a combined cycle engine. Accordingly, there remains a need in the art for a combined cycle engine having an improved combustor.